Patent GB-553558-A (GB)
Title: Improvements in or relating to cameras
IPC: G03B17/42
Filed: 1941-11-26
Abstract: 553,558. Photographic cameras. PURMA CAMERAS, Ltd., TERRETT, J., and WOOD, W. B. Nov. 26, 1941, No. 15253. [Class 98 (i)] A photographic shutter is wound through a pair of gear wheels which are normally held in engagement by resilient means but are positively moved out of engagement in a direction perpendicular to their axes of rotation when the driven gear reaches a predetermined position. Further, in a roll-film camera having a common winding member for the film and the shutter and means which normally lock it until rendered inoperative by the release of the shutter, an exposure indicator driven directly from the film prevents the locking means from locking the winding member except when the exposure indicator is in any one of the positions which it occupies after a filmwinding operation. The roll-film camera shown comprises a focal-plane shutter having front and rear blinds 32, 33 mounted on spring rollers 34, 35 and winding rollers 36, 37. The latter are driven by pinions 38, 39 engaging gears 40, 41 independently rotatable on a spindle 53. The gear 40 is driven by a pinion 42 carried by an arm 43 pivoted about the axis of the winding spindle 17 and engaging a gear 44 on that spindle. The pinion 42 is normally resiliently held in mesh with the gear 40 by a link 52 pivoted to the arm 43 and to a release lever 48, Fig. 7, which is pivoted at 51 and urged in an anticlockwise direction by a spring 102. On winding the shutter, from the unset position shown in Fig. 2 to the set position shown in Fig. 7, the spindle 17 is rotated by the winding knob and rotates the gear 40 through the pinion 42. When the shutter is nearly set, the pinion 42 engages teeth on an arcuate slotted deflector plate 97, slidably mounted on the gear 40 by screws 96 and covering a portion of its periphery which is unprovided with teeth. The teeth in the deflector plate 97 are of successively diminishing depth, so that the pinion 42 is moved gradually out of engagement and slips on the edge of the plate 97, which slides on the screws 96 against the action of a spring 99. The shaft 17 may thus be turned further to complete the winding of the film. During the setting of the shutter, a pin 89 on the gear 40 engages a pin 92 on the gear 41, so that the two gears rotate together to set both blinds. The shutter is held in the set position, Fig. 7, by a latch 49 pivoted at 105, the nose of which engages the pin 89. On pressing the release button 31, the release lever 48 is rocked, and through the link 52 moves the pinion 42 out of contact with the gear 40 and its deflector plate 97. At the same time the latch 49 is rocked to release the pin 89, and hence the front blind, but the pin 92 is held in a notch 109 of a second latch 50, shown separately in Fig. 6. When the front blind has moved a distance predetermined by the speed-setting of the shutter, a pin 94 moving with the gear 40 engages the nose 108 of the latch 50 and moves it to release the pin 92, and with it the second blind. The pin 94 is carried by a speed-setting disc 28 which can be moved axially against a spring 95 to engage the pin in one of a series of apertures in the gear 40, in order to vary the extent to which the first blind moves before release of the second. For " bulb" exposures the pin is so set that it does not engage the latch, which thus prevents release of the second blind until the button 31 is released. The film passes over a measuring roller 21, which through gears 60, 61, 63, 64 rotates an exposure indicator disc 65. When a new exposure length has been wound into position, a dog 82 on an arm 77 falls into a slot 83 in the disc, a link 75 pivoted at its ends to the arm 77 and to an arm 80 moving to the left and causing a dog 81 on the arm 80 to engage the gear 44 and so lock the winding shaft. When the shutter is released, an upward extension 89a of the pin 89 on the gear 40 engages one arm of a bifurcated cam member 85 and pivots it against the dead-centre action of a spring 113 to the position shown in Fig. 2. In this position a projection 119 on the cam engages a pin 117 on a lever 84 pivoted at 86 and coupled by a pin and slot connection to the link 75, so rocking the lever clockwise and moving the link 75 to the right to free the disc 65 and gear 44. During the rewinding movement the pin 89a engages the other arm of the cam 85 and rocks it anticlockwise through the dead-centre position, so causing a spring 118 to engage the pin 117 and force the lever 84, and with it the link 75, to the left, so that on completion of the winding the dog 82 falls into the next slot in the disc 65 and locks the winding-mechanism as before. The gears 61, 63 are carried on a spring-urged arm 62 which, together with the arm 77, may be moved by a rotatable cam member 69 away from the disc 65 to free it for continuous rotation when winding the end strips of the film. When the disc is thus free, a coiled spring (not shown) returns it to its initial position.